1. Field of the Invention
The invention relates to silane-containing polyvinyl alcohols and polyvinyl acetals, to processes for their preparation and to their use.
2. Description of the Related Art
The prior art discloses a series of processes for preparing silane-containing polymers. The preparation may be effected, for example, by means of polymer-like reaction of functional polymers with silylating agents. U.S. Pat. No. 5,036,137, for example, describes the preparation of silylated polyvinyl alcohol by reacting polyvinyl alcohol with 3-glycidoxypropyltrimethoxysilane or vinyltrimethoxysilane. EP-A 581576 discloses the reaction of OH-functional polymers such as polyvinyl alcohol with alkylorthosilicates or alkyltrialkoxysilanes.
Silane-containing polymers may also be prepared by means of copolymerization of silane-functional, ethylenically unsaturated monomers. EP-A 123927 relates to silyl-modified polyvinyl alcohols which are obtainable, among other routes, by copolymerization of vinyl esters with silyl-functional comonomers and subsequent hydrolysis.
A further route is the introduction of silane groups into the polymer by terminating the polymer chain with thio compounds containing Si groups, for example mercaptosilanes, as described in U.S. Pat. No. 6,346,570; or termination by means of Michael addition of functional silanes, as disclosed by U.S. Pat. No. 6,221,994. WO-A 01/09249 discloses the preparation of silane-functional copolymers by means of copolymerization with vinyl-silane and termination of the polymer chain with mercaptosilane. A disadvantage in the termination of polymer chains with mercaptosilanes is their toxicity and their tendency to add to double bonds. Furthermore, these mercaptosilanes have an excessively strong tendency to control the molecular weight, which is manifested in too great a reduction in the molecular weight. In addition, the reaction rate in the polymerization is frequently reduced. Further disadvantages in the use of mercaptosilanes are their tendency to yellowing and their unpleasant odor.
Silane-modified polyvinyl acetals are disclosed by four Japanese publications. JP-A 06-247760 and JP-A 06-248247 disclose polyvinyl acetals modified with silane-functional monomer units, which are used as binder for cement compositions or for inorganic fiber materials. These Si-modified polyvinyl acetals are obtained by copolymerizing vinyl acetate with vinylalkoxysilanes, subsequently hydrolyzing the vinyl ester-vinylsilane copolymers and finally acetalizing with aldehyde. JP-A 10-237259 relates to a mixture of silane-modified polyvinyl acetal with unmodified polyvinyl acetal for coating materials for printing with inkjet printers, for which vinyl ester-vinylsilane copolymers are initially hydrolyzed and subsequently mixed with unmodified polyvinyl alcohol in order to be acetalized with aldehyde. JP-A 62-181305 finally discloses a polyvinyl butyral modified with triethoxyisocyanato-propylsilane. In this case, the alkoxysilane group is linked to the polymer structure by polymer-like reaction via a urethane bond (by reaction of the isocyanate group of the silane with free hydroxyl groups on the polyvinyl butyral).
DE-A 10140129 discloses the acetalization of partly hydrolyzed or fully hydrolyzed vinyl ester polymers with silane-containing aldehydes.